I have a Pismo PowerBook that has no video for both the internal display and any attached external displays. It seems to boot up just fine as I can hear the hard drive working and can even put the computer to sleep by pressing the power button followed by the "s" key.

I initially thought that this must be a problem with the logic board, so I ordered a replacement and installed it. The new board produces exactly the same symptoms as before: no video from any source. Other than a dead replacement logic board, is there anything else that would cause this problem?